To generate electricity, hydraulic power, thermal power or atomic power is utilized, which involves disadvantages such as natural destruction with a dam, fuel shortage, air pollution and radioactivity injuries. Clean natural energy such as solar generation and wind power generation has been remarked over the whole world.
Wind power recovery rate by a windmill would be 45% in a horizontal shaft type and 35% in a vertical shaft type. Thus, in wind power generation, a horizontal-shaft-propeller-type windmill is mainly employed.
However, there are disadvantages as below. Unless wind at average wind velocity of 4 m/sec blows for over 2000 hours a year, it will not be profitable. Especially, in a large-size generator, unless wind of more than 7 m/sec blows, a windmill will not be rotatable. Wind at higher position blows faster. Hence it is necessary in a propeller-type wind power generator not only to increase the length of a propeller but also to increase height of a tower on which the generator is mounted. There are disadvantages in rigidity of a propeller, costs for transportation and installation, maintenance and place for installation.
In view of the disadvantages, an object of the invention is to provide a wind power generator, a windmill used therein, a main shaft and a blade where:                (1) generation rate in a small wind power generator becomes higher;        (2) a windmill is set or changed to the structure to achieve average wind velocity in geographical conditions of the installation place;        (3) the structure of the windmill can be changed after the wind power generator is installed;        (4) the light, high-rigidity windmill can be easily transported and assembled; and        (5) the wind power generator is made smaller to reduce cost and to expand selective range of the installation place.        